drm/display: move CEC_CORE selection to DRM_DISPLAY_HELPER

THe Kconfig symbol DRM_DISPLAY_DP_AUX_CEC is a boolean which simply
toggles whether DP_AUX_CEC support should be built into the
drm_display_helper (which can be eithera module or built-in into the
kernel). If DRM_DISPLAY_DP_AUX_CEC is selected, then CEC_CORE is
selected to be built-in into the kernel even if DRM_DISPLAY_HELPER is
selected to be built as a module. Move CEC_CORE selection to the latter
symbol in order to allow it to be built as a module.

Signed-off-by: Dmitry Baryshkov <[e-mail]>
Reviewed-by: Maxime Ripard <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/display/Kconfig

···
 config DRM_DISPLAY_HELPER
 	tristate
 	depends on DRM
+	select CEC_CORE if DRM_DISPLAY_DP_AUX_CEC
 	help
 	  DRM helpers for display adapters.
 
···
 config DRM_DISPLAY_DP_AUX_CEC
 	bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
 	select DRM_DISPLAY_DP_HELPER
-	select CEC_CORE
 	help
 	  Choose this option if you want to enable HDMI CEC support for
 	  DisplayPort/USB-C to HDMI adapters.